Hundreds of Newcastle supporters have been accused of causing trouble before one of the Premier League's most controversial matches of the season even kicked off.
The fans disrupted amateur matches being played near the away end of Wigan Athletic's DW Stadium by running on the pitches, dropping their trousers, ripping out the nets and trying to break the goals by hanging on the crossbars, a local official said.
They later boasted about the trouble they caused - including stealing a £65 match ball - on social networking sites.
The Premier League game on Sunday was won by the home side 2-1, but the result has been overshadowed by the fall-out from a tackle on Newcastle's Massaido Haidara by Callum McManaman.
The young Frenchman was stretchered off after the Wigan striker's challenge, which has been widely condemned but will not be punished by the FA.
Before the match, 250-300 Newcastle fans caused chaos after they got off coaches and wandered across to watch Wigan Cosmos play AFC Leigh Centurions in the South Lancashire Counties League, a Cosmos spokesman said.
"As the supporters spilled out of the coaches, which were not managed by the club or police officials, they proceeded to watch the game from the touchline," the official claimed.
"Some fans then chose to run on to the field of play, dropping their pants, causing the game to be stopped."
The situation then magnified as a crowd around 250-300 Newcastle United fans followed suit."
Although good-natured at first, the fans then started to rip out corner flags as they ran over the pitches and also took the match ball.
"We never recovered the ball, though we did manage to recover the corner flags."
The so-called fans then decided to charge over to the adjacent pitch where Goose Green Reserves were entertaining Olympic AFC in another South Lancashire Counties fixture.
"They again began by ripping out their corner flags."
The fans then charged into the goalmouth, jumping on to the goalposts in an attempt to snap the crossbar with the sheer numbers clambering on them."
They then started to rip the nets from the posts, tearing them and trying to take them. Our players helped to retrieve the nets."
After spending quite some time singing and hanging on the goalposts, the fans then ran back over to our pitch whilst singing 'We're Newcastle United, we'll do what we want'.
"The official claimed more damage was done to nets and corner flags."
Once again I would like to stress that, despite the obvious scenes developing, no support was provided from the authorities," the club spokesman said.
"This incident was a very distasteful experience that lasted for over 40 minutes and with families, dads, granddads and youngsters all watching the games as well as some quite experienced players who were all left shaken."
Cosmos put the cost of replacing the ball and the damaged nets at £200 - a tiny amount for a Premier League side but a lot of money for an amateur non-profit side, the spokesman said.
He added: "The fact that these same fans have taken to Twitter and YouTube to boast about the incident and in fact revelling in it, showing no signs of remorse, is possibly even more disturbing.
"Not only have they cost my football team a great deal of expense but they have shown a total disrespect to football itself.
"Pictures of Geordie fans hanging on posts and walking on the pitches appear on the Cosmos club website.